the treaty, signed in 1919, that officially ended World War I. The Treaty of Versailles, signed by Germany and the Allied Powers, forced Germany to pay enormous reparations, to substantially reduce the size of its military, and to recognize territorial changes that substantially reduced its land holdings. The treaty also established the League of Nations. The United States, represented by President Woodrow Wilson, played a crucial role in the treaty negotiations, but the U.S. Congress subsequently refused to ratify the treaty, based largely on opposition to American participation in the League of Nations.